This invention relates to a heat transfer tube for heat exchangers such as an air conditioner and a refrigerating machine, and, more particularly, to the structure of a heat transferring surface suitable for a single phase flow heat transfer tube having rows of projections therein.
In, for example, U.S. Pat. No. 3,734,140, a heat transfer tube is provided in a heat exchanger such as an air conditioner or a refrigerating machine, with the heat transfer tube having projections formed by forming primary grooves with a rolling plug inserted into the inside wall of the tube and thereafter further forming secondary grooves by additional machining, as well as a smooth tube having the inner surface structure which has not been subjected to any machining.
If a heat transfer tube having projections is used as a single phase flow heat transfer tube, much force for driving fluid is required because the configuration of the projections is not rounded but has acute angled corners, whereby a separation vortex is produced by a flow component which turns the corner, as will be described in detail later, whereby the fluid suffers a pressure loss between the inlet and outlet of the heat transfer tube. In addition, with respect to the faces of the projections which are perpendicular to the streamline of fluid, the fluid stagnates at those portions and the kinetic energy constitutes the collision pressure, whereby the portions become worn in over long period of time. This wear varies the height and configuration of the projection from its optimum values, and hence the initial heat transfer performance cannot be maintained. Furthermore, it is necessary to form the primary and secondary grooves in this method of using the rolling plug, which leads to an increase in machining steps and hence a rise in costs. It is also inconvenient that the dimension of projection which brings about the maximal effect on heat transfer is unobvious. In spite of the necessity for investigation by systematic experiments on the optimum values of the height, circumferential pitch and the pitch in the axial direction of projections, such values as might serve as parameters influencing heat transfer performance have not been made clear.
Accordingly, the aim underlying the present invention resides in solving the above-described problems of the structure of the inner wall of a heat transfer tube experienced in the prior art, and to provide the structure of a heat transferring surface of a heat transfer tube with projections having an optimum configuration numerically determined such as to provide the maximum transfer heat performance.
To achieve the aim, according to the invention the structure of a heat transferring surface is provided which is efficient in terms of heat transfer performance and is realized by forming a row of projections on the inner surface of a tube, the height of the projections ranging from 0.45 mm to 0.6 mm, the circumferential pitch ranging from 3.5 mm to 5 mm, and the pitch in the axial direction ranging from 5 mm to 9 mm, by pressing a rolling disc having a row of projections on the outer periphery thereof.
The above aim and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.